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Inorg. Chem. 1992, 31, 5484-5493

5484

A Hydrogen Atom in an Organoplatinum-Amine System. 2.' The First Isolated Arylplatinum(1V) Hydrides: Synthetic and Theoretical Study (SCF and CAS-SCF Calculations) on Model Complexes with a N-M(IV)-H/M(II)--*H-N+ Unit (M = Pd, Pt) Ingrid C. M. Wehman-Ooyevaar,t David M. Grove,t Peter de Vaal,* Alain Dedieu,* and Gerard van Koten'*t Department of Metal-Mediated Synthesis, Debye Research Institute, University of Utrecht, Padualaan 8, 3584 C H Utrecht, The Netherlands, and Laboratoire de Chimie Quantique, UPR 139 du CNRS, Universitt Louis Pasteur, 4, rue Blaise Pascal, F 67000 Strasbourg, France Received August 7, 1992

The reaction of cis-Pt( I - C ~ O H ~ N M ~ ~ - ~with - C Me2SnX2 , N ) ~ ( x = c1, Br) in C6H6 or a mixture of CH2C12 and t-BuOH affords the novel Pt(1V) hydride complexes PtX(H)(l-CloHaNMe2-8-C,N)2 (X = C1, Br) by a process involving intramolecular H abstraction from an SnMe grouping. Starting from C ~ S - P ~ ( C ~ H ~ C H ~ Nand M~~-~-C, MezSnBrz, one also initially obtains a Pt(1V) hydride complex, but this then isomerizes to the zwitterionic hydrogenbridged complex PtBr(C6H&H2NMe2-2-C,N)(C6H4CH2NHMe2-2-C,H).' The Pt(1V) hydride complex Pt(OOCCF3)(H)( ~ - C I O H ~ N M ~ ~ -is~ obtained - C , N ) ~from the reaction of cis-Pt( ~ - C I O H ~ N M ~ ~ - ~with - C ,the N)~ organic acid CF3COOH. However, with HCI, the zwitterionic hydrogen-bridged complex PtCI( l-CloH6NMe28-C,N)(l-CloHsNHMe2-8-C,H) (6(NH) = +15.9 ppm, 1J('95Pt,iH)= 180 Hz, IJ(15N,1H)= 59 Hz) is formed. The Pt(1V) hydride complexes, which are unstable in solution, are characterized by a IH NMR hydride resonance of ca. -20 ppm with 1J(19SPt,1H) 1600 Hz and a v(Pt-H) IR band at ca. 2280 cm-l. A mechanistic study of the formation of the hydride versus the zwitterionic hydrogen-bridge complexes shows the Lewis basicity of the anion to be an important factor. Molecular orbital (SCF and CASSCF) calculations on a model system (with Pd instead of Pt) show that the zwitterionic hydrogen Pd(I1) complex [PdCl(Me)2(NH3)--H-NH3] is more stable than its Pd(1V) hydride tautomer [PdCI(H)(Me)2(NH3)-NH3]. The stability of the former complex is mainly caused by favorable electrostatic interactions between the anionic palladium and cationic ammonium N H units, orbital interactions playing only a minor role. The reactivity of the Pt(1V) hydrides and the zwitterionic hydrogen-bridge complexes toward alkynes is described. Highly activated dimethyl acetylenedicarboxylate reacts with Pt(OOCCF3)(H)( 1- C I O H ~ N M ~ ~ - ~as - Cwell , N )as~ Pt(OOCCF3)( ~ - C I O H ~ N M ~ ~ - ~l-CloHaNHMe2-8-C,H), -C,N)( both containing the weakly coordinating anion OOCCF3, to afford the same "insertion" product Pt(OOCCFp){+ C(COOMe)=CH(COOMe))( I - C I O H ~ N M ~ ~ - ~ - C , N ) ~ .

=

Introduction Many reactions that are catalyzed by transition metal complexes involve interactions between hydrogen and the metal centerse2Besides side-on H2 bonding,3both terminal and bridging hydride bonds are known? and many examples of the so-called agostic M-.HX (three-center two-electron) interactionhave been r e p ~ r t e d . ~However, .~ there are only a few known examples of an intramolecular M-H-N (three-center four-electron) interaction.'~~-~ In this interaction, in contrast to the three-center two-electron interaction, an electron pair of a filled metal orbital To whom correspondence should be addressed. University of Utrecht. t Universitd Louis Pasteur. (1) Part 1: Wehman-Ooyevaar, I. C. M.; Grove, D. M.; Kooijman, H.; van der Sluis, P.; Spek, A. L.; van Koten, G. J . Am. Chem. SOC.1992, 114, +

9916. (2) (a) Parshall, G. W. Homogeneous Catalysis; Wiley: New York, 1980. (b) Darensbourg, M. Y.;Ash, C. E.Ado. Organomet. Chem. 1987,27, 1. (3) (a) Crabtree, R. H.; Hamilton, D. G. Ado. Organomet. Chem. 1988,28, 299 and references cited therein. (b) Kubas, G. J. Acc. Chem. Res. 1988, 21, 120. (c) Crabtree, R. H. Acc. Chem. Res. 1990, 23, 95. (4) (a) Bau, R.;Teller, R. G.; Kirtley, S. W.; Koetzle, T. F. Acc. Chem. Res. 1979,12, 176. (b) Bullock, R. M.; Casey, C. P. Acr. Chem. Res. 1987, 20, 167. ( 5 ) A n k h C. G.; Pregosin, P. S . Mugn. Reson. Chem. 1985, 23, 671. (6) (a) Carr, N.; Dunne, B. J.; Orpen, A. G.; Spencer, J. L.J. Chem. SOC., Chem. Commun. 1988,926. (b) Brookhart, M.; Green, M. L. H.; Wong, L.-L.Prog. Inorg. Chem. 1988, 36, 1. (7) Hedden, D.; Roundhill, D. M.; Fultz, W. C.; Rheingold, A. L. Organometallics 1986, 5, 336. (8) Brammer, L.; Charnock, J. M.; Goggin, P.L.; Goodfellow, R. J.; Orpen, A. G.; Koetzle, T. F. J . Chem. SOC.,Dalton Trans. 1991. 1789.

0020-1669/92/133 1-5484503.00/0

(e& dzz) is also involved. The only theoretical investigationsof these M-OH-N interactions are the molecular orbital calculations carried out on a model system of the dl0 nickel complex [(Hnp3)NiCO] [BPhd] (Hnp3 = NH(CH2CH2PPh2)3).I0 These calculations, carried out at the extended Hiickel level, could not evaluate the magnitude of the electrostatic component of the interactions. The relationship between Mn--H-N interactionsand tautomeric H-M"+2-N (metal hydride) systems is in this context extremely relevant. Most transitionmetal hydridecomplexes are synthesized directly from appropriate acids. Such reactions with d8 organometallic complexes can proceed in several ways: (i) by an oxidative addition reaction to the metal center (qla)," (ii) by electrophilic attack on a metal-carbon bond (eq 1b),12or (iii) by reaction at the ligand (qlc).I3 In a previous communication we reported that Pt(1V) hydride complexes PtX(H)(1-C10H6NMe2-8-C,N)2 (X= C1, Br) can be synthesized from the reaction of cis-Pt(I - C I O H ~ N M ~ ~ - ~ - C , N ) ~ (9) Wehman-Ooyevaar, 1. C. M.;Grove, D. M.; van der Sluis, P.;Spek, A. L.; van Koten, G. J. Chem. Soc., Chem. Commun. 1990, 1367.

(IO) Cecconi, F.;Ghilardi, C. A.; Innocenti, P.; Mealli, C.; Midollini, S.; Orlandini, A. Inorg. Chem. 1984, 23, 922. ( 1 1) (a) Blake, D. M.; Kubota, M. Inorg. Chem. 1970,9,989. (b) Crabtree, R. H.; Quirk, J. M.;Fillebeen-Khan, T.; Morris, G. E. J. Organomet. Chem. 1979, 181,203. (c) Imhoff, P.;Nefkens, S.C. A.; Elsevier, C. J.; Goubitz, K.;Stam. C. H. Organometallics 1991, 10, 1421. (12) (a) Romeo, R.; Minniti, D.; Lanza, S.;Uguagliati, P.:Belluco. U. Inorg. Chem. 1978,17,2813. (b) Belluco, U.; Michelin, R. A.; Uguagliati, P.; Crociani. B. J . OrPonomet. Chem. 1983. 250. 565. (13) Crociani; B.; Di BLnca, F.; Giovenco, A:; Scrivanti, A. J . Organomet. Chem. 1983, 251, 393.

Q 1992 American Chemical Society

An Organoplatinum-Amine System LM"

+

HX

LM"-CR~ +

HX

+

HX

LM"

-

-

Inorganic Chemistry, Vol. 31, No. 26, 1992 (la)

LM"*'(x)(H)

LM"(X)

+

[(LH)'M"]X'

HCR~

(1b) (IC)

with MezSnXz (X = CI, Br) in an aprotic ~olvent.~ We now show that this type of Pt(1V) hydride complex can also be obtained in a conventional reaction type, Le. by oxidative addition of HX. However, this method is only successful with CF3COOH. With HCl, the zwitterionic hydrogen Pt(II)--H-N+ complex PtCl( 1CloH6NMe2-8-C.N)( l-Cl0HaNHMe2-8-C,H) is obtained; this complex is a tautomer of the correspondingR(1V) hydride species. The mechanisms that lead to either a Pt(1V) hydride or the tautomeric Pt(I1)-.H-N system and the interrelationshipbetween these tautomers are the subject of the present paper. Their electronicstructure and their relative stability have been analyzed through ab-initio SCF and C A S S C F calculations carried out on the [PdCl(H)(Me)2(NH3).-NH3] and [PdCl(Me)2(NH+HNH3] model systems and on the Pt analogs. It is shown that favorable electrostatic interactions play a major role in the stabilization of the zwitterionic hydrogen complex. The reactivity of both types of complexes toward unsaturated reagents has also been studied, and with dimethyl acetylenedicarboxylate both complex types give the same Pt(1V) product; a mechanism involving electron transfer is proposed to explain this result.

Experimental Section ceaerrlproeedures. Syntheseswerecarriedout usingstandardSchlenk techniques in an atmosphere of purified nitrogen. All solvents were dried and distilled under nitrogen prior t o w . The compoundscis-Pt( l-ClOH6NMe2-8-Cfl2,I4 C ~ ~ - P ~ ( C ~ H ~ C H Z N M ~ Z - ~ cis,cis-PtBrz( - C , N ) ~ , ' S1Cp&NMer8-C,N)2,16 and PtX( ~ - C I O & N M ~ - ~ - C , N I-CI )( W H M e 2 8-C,H) (X = CI, Br, 00CCF3)l were prepared by literature methods. IH and I3C NMR spectra were recorded on a Bruker AC 200 spectrometer. Infrared spectra were recorded on a Perkin-Elmer 283 infrared spectrophotometer. Elemental analyses were obtained from the Section Elemental Analyses of the Institute For Applied Chemistry TNO, Zcist, The Netherlands. Synthesis of PtCI(H)(l-Cld&NMq-S-C,N)2 (la). To a yellow suspensionofcis-Pt( l-CloH6NMe2-8-C,N)2 (0.5g;0.93 mmol) in toluene (40mL) was added a solution of Me2SnCl2 (0.21 g;0.94 mmol) in toluene (5 mL). The suspension slowly became clearer, and after 1 h of stirring, a clear solution was obtained. This solution was stirred for 5 days, after which time a white solid had precipitated. The solid was collected by filtration, washed with hexane (20 mL), and dried in air, affording l a as an off-white powder (0.35 g; 66% yield). Infrared spectrum in KBr: u(N-H) at 2280 cm-'. Evaporation in vacuoof the toluene filtrate to dryness afforded a yellow powder. According to IH NMR data, this was a mixture of unreacted cis-Pt( 1-C1oH6NMe2-8-ClN)2 and MeZSnC12. Synthesis of PtBr(H)(l-Cl&NMq-l-C,N)2 (lb). a. To a stirred yellow suspension of cis-Pt( I - C I O H ~ N M ~ ~ - ~ - (0.4 C , Ng;) ~0.75 mmol) in C6H6 (40 mL) was added a solution of MeZSnBrz (0.24 g; 0.78 mmol) in C6H6 (5 mL). The suspension slowly became clearer, and after 1 h, a clear solution was obtained. After another hour of stirring, a solid began to precipitate and the mixture was stirred for a further 60 h. The solid was collected by filtration and dried in air to afford pure Ib as an off-white powder (0.2 g; 43% yield). Anal. Calcd for Cz4HzsBrNzPt: C,46.76;H,4.09;N,4.54;Br, 12.96. Found: C,46.29;H,4.09;N,4.44; Br, 14.45. Infrared spectrum in KBr: u(Pt-H) at 2275 cm-I. Evaporation in vacuo of the C6H6 filtrate to dryness yielded a yellow powder. According to IH NMR data, this was a mixture of four compounds, Le. Ib, cis-Pt( I - C I O H ~ N M ~ Z - ~ - CMezSnBr2, ,N)~, and PtBr(SnBrMe& 1- C I O H ~ N M ~ ~ - ~ - C , N ) ~ . (14) Wehman, E.;van Koten,G.; Knaap, I. C.; Ossor, H.;Pfeffer, M.; Spek, A. L. Inorg. Chem. 1988, 27, 4409. ( 1 5 ) Longoni, G.; Fantucci, P.; Chini, P.; Canzioni, F. J. Orgcmomet. Chem.

5485

b. With C6D6 as solvent. The procedure is the same as described in mL )~ method a, starting with 0.27 g of cis-Pt( ~ - C I O H ~ N M ~ Z - ~in- C20, N of C6D6. The suspension was filtered after 18 h of stirring, and the solid was identified as a 5:l mixture of l b and PtBr( I - C I O H ~ N M ~ ~ - ~ - C 1- , N ) ( CloHsNHMe2-8-C,H) (total yield: 0.1 g; 33%). c. Toa stirred yellow solution o ~ c ~ ~ , c ~ ~ - P ~ B ~ ~ ( ~ - C I O H ~ N M (0.22 g; 0.32 "01) and a catalytic amount of azobis(isobutyronitri1e) in CHzC12 (25 mL) was added n-BuoSnH (87 pL; 0.32 mmol). After 2 min, the solution was evaporated in vacuo to an oily residue. Upon addition of Et20 (20 mL) and 0.5 h of stirring, a solid precipitated. This was isolated by filtration and dried in vacuo to afford l b as an off-white powder (0.1 1 g; 55% yield). d. A solution of MezSnBr2 (0.31 g; 1 mmol) in CH2C12 (7 mL) was added to a stirred yellow solution of cis-Pt( ~ - C I O H ~ N M ~ Z - ~ -(0.54 C,N)Z g; 1 mmol) in a 6:1 (v/v) mixture of CHzCl2 and 1-BuOH (35 mL). After 3 h, the dark solution was evaporated in vacuo to a brownish powder. This solid was suspended in C6H6 (15 mL), and the suspension was stirred for 30 min. The solid was collected by filtration, washed with C6H6 (5 mL), and dried in air to afford a 5:l mixture of l b and PtBr(l-c10H6NMe28-C,N)(l-CloH6NHMe2-8-C~(total yield: 0.25 g; 41%). Reactim of cisPt(l-Cl&NMq-8-C,N)2 with M q S d r 2 in CHICI2/ROH. The same procedure as described for the synthesis of Ib, method d, was followed using ROH(D) (MeOH(D), EtOH, CF3CH2OH, and 1-BuOD) instead of t-BuOH. The products were washed with C6H6 (t-BuOD), Et20 (EtOH, CFBCHZOH),or hexane (MeOH(D)). The types of products and yields are shown in Table 11. R m ~ t Oif ~c & P ~ ( ~ - C ~ & N M ~ ~ - nith CJV PhzSacl2 )~ iII TOIIWR. A solution of PhzSnClz (0.27 g; 0.8 mmol) in toluene (6 mL) was added to a stirred yellow suspension of cis-Pt(l-CloHsNMe2-8-C,N)2 (0.42 g; 0.8 mmol) in toluene (35 mL). After 4 h, a slightly turbid solution was obtained, which was stirred for another 5 days. The solvent was then removed in vacuo to afford a sticky residue. After addition of hexane (25 mL), a yellow solid was obtained. This was collected by filtration and washed once with hexane (10 mL). Drying in air afforded a yellow powder, which was according to IH NMR data a mixture of cis-Pt( 1CIOH~NM~~-~-C and , NPtCI(SnClPhz)( )~ l-CloHsNMe2-8-C,N)2 with other unidentified products. Reactionof cis-Pt(Cr)4CH2NMcrtC~wiRLthM~r2inBeazene. To a stirred white suspension of C~S-P~(C~HICHZNM~Z-~-C,N)Z (0.7 g; 1.5 mmol) in benzene (40 mL) was added a solution of Me2SnBr2 (0.47 g; 1.5 mmol) in benzene (6 mL). The suspension became clearer, and after 0.5 h a 3-mL sample was taken and evaporated in vacuo to afford an off-white powder. According to 'H NMR data, this was a mixture ~ - ~ - C , NPtBr(BrSnMez)(C6H4)~, of C ~ ~ - P ~ ( C ~ H ~ C H Z N M ~MezSnBrZ, CHzNMer2-Cfl2, and PtBr(C&CHzNMer2-C,N)(C&CH2NHMer 2-C,H).l The slightly turbid benzene solution was stirred for another 48 h. After this time, the mixture was filtered. The resulting white solid (0.19 g) was identified by its IH NMR data as unreacted CiS-Pt(C6H4C H ~ N M ~ Z - ~ - C , NThe ) Z .yellow benzene filtrate wasevaporated in vacuo to an off-white powder, which was identified by its IH NMR data as a mixture of PtBr(C&CH2NMer2-C,N)(C&CH2NHMe2-2-C&), MSnBr2, and a tin-containing product. The powder was resuspended in CHzClz (5 mL), and Et20 was added (20 mL). After stirring of this mixture for 0.5 h, the solid was isolated by filtration and dried in air to as an offafford P~B~(C~H~CH~NM~~~-C,N)(C~HICH~NHM~~-~-C& white powder (0.48 g; 60% yield). Reaction of c i s P t ( C ~ J W I q - 2 - C , N ) 2with M e r 2 in CH2Cl2/t-BPOH. To a solution of C ~ ~ - P ~ ( C ~ H ~ C H Z N M(0.45 ~ ~ - ~g;- C , N ) ~ 1 mmol) in a 1O:l (v/v) mixture of CH2C12/r-BuOH (33 mL) was added a solution of MezSnBr2 (0.31 g; 1 mmol) in CHzC12 (5 mL). The suspension was stirred for 5 h and then evaporated in vacuo to afford an off-white powder, which was identified by its IH NMR data as a mixture of P~B~(C~)~CH~NM~~-~-C,N)(C~HICH~NHM~~~-C&), Cidt(C6)4CHzNMe2-2-C,N)z, Me2SnBr2, P ~ B ~ ( B ~ S ~ M ~ ~ ) ( C ~ H I C H Z N M ~ ~ - ~ C,N)2, and a tin-containing product. The powder was redissolved in a 1O:l (v/v) mixture of CH2C12/?-BuOH (33 mL), and the solution was stirred for 18 h, after which the resulting suspension was filtered. The yellow filtrate was concentrated in vacuo to 2 mL, and Et20 (15 mL) was added. After stirring of this suspension for 0.5h, the solid was collected by filtration and dried in air, affording PtBr(CsH4CH2NMez-2C,N)(C~H~CH~NHM~Z-~-C,H) as an off-white powder (0.41 g; 75% yield). Reactionof M m r 2 with I-BUOH. To a solution of Me2SnBrz (0.03 g; 0.1 mmol) in CDCI3 (0.5 mL) was added a 4-fold excess of C6H5CH(Me)NMe2 and then an exccss of t-BuOH. The solution was

5486 Inorganic Chemistry, Vol. 31, No. 26, I992

Wehman-Ooyevaar et al.

basis sets: Pd (16,11,9) [contracted to 7,5,5], CI (11.7) [4.3], C and N subsequently monitored with IH NMR spectroscopy and followed in time. No reaction was observed. ( 9 5 ) [3,2], H(4) [2], hydride or bridging H (6,l) [3,1].20923 For calculations on the Pt complex, use was made of the RECP of Hay and Reaction of cisPt(l-CloHrNMe2-8-C,N)2 and CF3COOH. For a Wadtz'with a (3,3,3) [2,2,3] basis setz5for Pt and the ECP of Barthelat typical NMR experiment, a yellow solution of ca. 25 mg of cis-Pt(1et a1.26with a (4.4) [3,3] basis set for Cl. Details of the geometries were CloH6NMe2-8-C,N)zin1 mLofdryCDCl3wasprepared. To thissolution mostly derived from the X-ray crystal structure of PtBr( 1-CloH&"e2was added CF3COOH in the following amounts: 0.5, 1, 1S , and 2 equiv 8-C,N)( I - C ~ O H ~ N H M ~ ~ - ~and - Cfrom , H ) ~reported average palladiumand an excess (0.1 mL). The 'H NMR spectra of the resulting pale ligand bond This yielded the following bond lengths and bond brownish solutions were subsequently recorded and followed in time. In angles: Pd-C = 2.03 A, Pd-N = 2.04 A, Pd-CI = 2.33 A, Pd-H = 1.61 all experiments, IC was the main product and only traces (1-5%) of A, C-H = 1.07 A, H-C-H = 109.5', N-H = 1.023 A, H-N-H = Pt(OC)CCF3)( I - C ~ & , N M ~ Z - ~ - C ,l-Cl&,NHMer8-C,H) N)( were seen.[ 114.2O. For the free NH3, N-H was set to 1.01 A and the angle H-N-H Reactiomof 1amlPtX(l-C1oHsNMg8-f3)( I-CI&JVHM&-CJI) to 107O. A tetrahedral geometry was assumed for NH4+ with N-H = (X = Br, OOCCF3) witb Alkenes and Alkynes. For a typical NMR 1.02 A. In the Pd(1V) hydride system, the NH3 molecule was put at 10 experiment, an excess of the unsaturated reagent (ethene, styrene, A from the hydride ligand; see F i n Chart I. In the Pd(II)-H-N system neohexene, methyl methacrylate, vinyl acetate, dimethyl maleate, the Pd-N and Pd-H distances of the Pd-H-NH3 linkage were optimized pheny lacetylene, diphenylacetylene, or dimethyl acet ylenedicarboxylate) to 3.03 and 2.01 A, respectively, in good agreement with the X-ray crystal was added to a solution of ca. 5 mg of one of the Pt complexes l b or structure of the Pt system9 (see A in Chart I). The other geometrical PtX( I - C ~ , J H ~ N M ~ ~ - ~ - CI-C~OI-I~NHM~~-~-C,H) ,N)( (X= Br,OOCCFs) parameters were kept constant. Although a geometry optimization might in 0.7 mL of dry CDCl3. The solution of ICwas prepared by addition change somewhat the relative energies of the various isomers, it should of an excess of CF3COOH to a solution of cis-Pt( I-CIOH&"~~-~-C,N)Z not alter our conclusions on their relative positioning and on the nature in CDCl3. IH NMR spectra were subsequentlyrecorded and then followed of the metal-H-N linkage. Moreover it has been experimentally found in time. Only in the case of l e and Pt(OOCCFn)(I-CloH6NMe2-8that the bond lengths in the Pd(II)-H-N system were comparable to the C,N)( 1-CloH6NHMe2-8-C.H) with dimethyl acetylenedicarboxylate was ones in the system without this interaction.[ In addition to these two a new product formed. In both cases this was P~(OOCCF~){T$geometries, a few others shown in Chart I and characterized by various C(COOMe)=CH(COOMe)]( I - C I O H ~ N M ~ Z - ~ - C(3). ,N)Z Pd-H and N-H bond lengths were also investigated. The use of a MC'H NMR (CDCl3, 24 "C): 8 2.09 (s, -NCHj, 3J(195Pt,lH)= 16.2 SCF type wave function (here C A S S C F ) was found to be necessary to Hz), 2.75 (s,-COOCH~),3.12 (s,-NCH~, 3J(195Pt,'H)= 7.8 Hz), 3.45 obtain a reliable description of the electronic structure of the Pd(IV) (s, -NCH3, 3J(195Pt,'H) = 14.4 Hz), 3.62 (s, -COOCH3), 3.68 (s, hydride complexes and of the associated energetics. On the other hand, -NCH3), 5.71 (d, 2-HofAr, 3J(1H,lH)= 6.5 Hz, 3J(195Pt,lH)= 48 Hz), the SCF wave functions turned out to be a reasonable description of the 6.5 (s, C=CH, 3J(195Pt,lH)= 77 Hz), 6.76 (t, 3-H of Ar, )J(IH,lH) = Pd(I1) complexes and of the zwitterionic hydrogen Pd(I1) systems. For 6.5 Hz), 7.13 (d, H o f A r , 3J(1H,1H)= 6.5 Hz), 7.2-7.8 (m, H o f Ar), this reason the platinum calculations (which were of SCF type) were also 8.08 (d, 2-H of Ar', 3J(1H,LH)= 6.5 Hz, 3J('95Pt,1H)= 51 Hz). limited to the Pt(I1) and the zwitterionic hydrogen Pt(I1) systems. The "%n NMR Measurements. II9Sn NMR spectra were recorded on a geometries were not reoptimized at the C A S S C F level. Such an Bruker AC 200 spectrometer operating at 74.63 MHz. Chemical shifts optimization would probably not change the relativeenergies of thevarious in ppm are relative to external SnMe4. The complex Ir(@-BrSnisomers to a greater extent. It has been shown by Siegbahn and coBrMe2)(C6H4CH~NMez-2-C,N)(cycloocta-l,5-diene) was prepared by workers that the potential energy surfaces for the Pd-H and the Pd-L literature methods.[' The complex PtBr(SnBrMe2)( 1-CloH6NMez-8bonding are quite flat around the equilibrium bond lengths and that C,N)2 (2) was prepared by mixing cis-Pt(I - C ~ O H ~ N M ~ Z - ~ - C (0.22 ,N)Z geometry optimization is not expected to change thecalculated interaction g; 0.4 mmol) and MezSnBrZ (0.12 g; 0.4 mmol) in CD2C12 (3 mL) and energies very muchSz8 placed in a 10 mm 0.d. tube. For the separatestudy of the tin-containing byproduct, a nonpurified material obtained from the filtrate from the Result8 reaction of cis-Pt( l-CloH6NMez-8-C,N)z with Me2SnBrz (synthesis of A. Formstioa rad Cbaracterizatioa of the Pt(IV) Hydride lb, method a) was used. Complexes P~X(H)(~-CI&NM~~-~-C,N)I (14X = 0, lb, X = Il9Sn NMR data (CDzC12, 24 "C) for the three complexes are as Br). When the Pt(I1) complex cis-Pt(l-CloH6NMe2-8-C~2 is follows. Ir(p-BrSnBrMe2)(C6H~CH~NMe~-2-C,N)(cycloocta-1,5treated with Me2SnX2 (X = C1, Brl in drv CH7C1, or CAHA diene): 6 -161.6 (br s). Mixture of cis-Pt(l-C10HsNMez-8-C,N)z and (C6D6), the new Pt(1V) hydrides PtX(H j(1-CliHiNMe;-8: = 13 070 Hz, MezSnBrz: 8 56.8 (s, MezSnBrz), 4 9 . 2 (s, 1J(195Pt,119Sn) 2). -72.4 and -1 19 (2 X s, tin-containing byproduct). Tin-containing C,N)2 (la, X = C1; lb, X = Br) are formed after 4 days in byproduct: 6 -72.4 (s, J(195Pt,119Sn) = 67 Hz), -119 (s, J(lg5Pt,ll9Sn) reasonable yields; see eq 2 in Scheme 1. Complex Ib can also be = 67 Hz). formed by an alternative route in which cis,cis-PtBrZ(I-CloHGTechnical Details of the MO Calculations. SCFls and CAS-SCFl9 NMe2-8-CJV)2is reacted with n-BuJSnH (eq 3). Treatment of calculations were carried out on the irans- [PdCI(H)(Me)2(NH+NH,1 cis-Pt( I - C I O H ~ N M ~ ~ - ~ with - C , NPhzSnCl2 )~ does not afford a systems, which serve as models and truns-[PdCI(Me)2(NH3).-H-NH,I Pt(1V) hydride but, instead, affords a complex that contains, on refor l a and P~CI(~-C~~H~NM~~-~-C,N)(I-CI~H~NHM~~-~-C,H), the basis of IH NMR data, a R S n moiety. Such a complex spectively. The simplifications made leading to the model complex, i.e. with a P t S n moiety, PtBr(BrSnMez)(l-CloHsNMe2-8-C,N)2 Pd instead of Pt, Me and NH3 ligands instead of the large CloH6NMez-8 (2), was also observed by 'H NMR spectroscopy as an intergroups, and the symmetric trans geometry instead of the asymmetric cis mediate in reaction 2. geometry, all serve to reduce computation time into a workable range. In order to verify whether the calculations on complexes with the trans (20) Veillard, A.; Dedieu, A. Theor. Chim. Acta 1984,65,215. The original geometry yield results comparable to those on the cis models, we carried (15,9,8) basissetwasmodified bytheadditionofansprimitiveofexponent out a few representative calculations on the latter. We also checked 0.305 60 to suppress the gap between the functions needed to describe whether the calculations on the Pd complex are comparable with those thewidelyseparated4sandSsshells, twopfunctionsofexponents0.235 60 on the same model with Pt as the metal. In order to do this, we performed and 0.083 86 to describe the Sp shell, and one d function of exponent 0.078 90. These exponents were chosen according to the even-tempered some calculations at the SCF level using for the Pt atom a relativistic criterion. effective core potential (RECP). Use was made of the following Gaussian (21) Hyla-Kryspin. I.; Demuynck, J.; Strich, A.; Etnard, M.J. Chem. Phys. 1981, 75, 3954. (22) Huzinaga,S.Technical Report, University of Alberta, Edmonton, 1971. ( 1 7) vander Zeijden, A. A. H.; van Koten, G.; Wouters, J. M. A.; Wijsmuller, W.F. A.; Grove, D. M.; Smeets, W. J. J.; Spek, A. L. J. Am. Chem. (23) Huzinaga, S.J. Chem. Phys. 1965, 42, 1293. SOC.1988, 110, 5354. (24) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (1 8) (a) Ernenwein, R.; Rohmer, M. M.; Btnard, M. Comp. Phys. Commun. (25) Jeung, G. H.; Liddell, M. Private communication. 1990.58, 305. (b) Rohmer, M.-M.; Demuynck, J.; Btnard, M.; Wiest, (26) Bouteiller, Y.;Mijoule, C.; Nizam, M.; Barthelat, J. C.; Daudey, J. P.; R. Comp. Phys. Commun. 1990.60,127. (c) Wiest, R.; Demuynck, J.; Pelissier, M.; Silvi, B. Mol. Phys. 1986, 65, 295. BCnard, M.; Rohmer, M.-M.; Ernenwein, R. Comp. Phys. Commun. (27) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, 0.;Watson, D. G.; 1991, 62, 107. Taylor, R. J. Chem. Soc., Dalron Trans. 1989, S1. (19) (a) Roos,E. 0.; Taylor, P. R.; Siegbahn, P. E. M. Chem. Phys. 1980, (28) (a) Blomberg, M. R. A.; Schhle, J.; Siegbahn, P. E. M.J. Am. Chem. 48, 157. (b) Siegbahn, P. E. M.; AlmlBf, J.; Heiberg, A.; Roos, B. 0. Soc. 1989, 11 I , 61 56 and references cited therein. (b) Blomberg, M. J . Chem. Phys. 1981,74,2384. ( c ) Roos, B. 0.In?. J. Quantum Chem., R. A.; Siegbahn, P. E. M.; Nagashima, U.; Wennerberg, J. J. Am. Quanrum Chem. Symp. 1980, 14, 175. Chem. SOC.1991, 113, 424.

An Organoplatinum-Amine System

Inorganic Chemistry, Vol. 31, NO.26, 1992 5487

complex cis,cis-PtBrt( 1- C I O H ~ N M ~ ~ - ~ -and C , Nn-Bu3SnH )~ (reaction 3). The presence of a terminal hydride ligand in l a and l b is confirmed by their IR spectra (see Experimental Section) that show sharp absorption bands at 2280 and 2275 cm-', respectively. These values are consistent with literature data for terminal hydrides (2300-1900 cm-I) and exclude the possibility that 1 is a dinuclear species with a bridging hydride (v(M-H-M) = 1600-1500 ~ m - l ) .In ~ ~complexes 1, the two C,N bonded naphthyl ligands and the hydride occupy five coordination sites; the sixth is occupied by an anion (Cl, la; Br, l b CF,COO, IC). Detailed analysis of the IH NMR spectra of 1 allows us to propose 1C (X = OOCCF,) the specific geometric structure for these complexes shown in Scheme I. The possible position of the halide, for example, can be deduced from the fact that there is no downfield shift of the second naphthyl ortho proton; Le, this proton is not in the The IH NMR spectrum of the tin-containing byproduct of neighborhood of the halide. If this halide had been positioned reaction 2 contains two broad multiplets at ca. 3.5 and 1.3 ppm, near an ortho proton, the latter would be expected to show a while the Il9Sn NMR spectrum shows two singlets at -72 and downfield shift as in, for example, cis,cis-PtBrz(l-CloH6NMe2-1 19 ppm, both with platinum satellites (J(195Pt,119Sn) = 67 Hz) 8-C,N)2.16 Therefore, the second ortho proton is held near the (see Experimental Section). According to the stoichiometry of hydride. The proposed structure is closely related to that of the reaction 2, this byproduct should be based on a tin-carbene tautomer of 1, Le. PtX( ~ - C I O H ~ N M ~ ~ - S -l-CloH6NHMe2C,N)( complex, [SnX(CH2)(Me)], but platinum is also present; un8-C,H).l However, the IH NMR spectrum of the latter is fortunately, full characterization of this material was not remarkably different and shows, instead of the upfield hydridic successful.29 resonance, a very low field protonic resonance at 15.8 ppm. Complexes 1 are stable in the solid state, but in solution 'Hand *19SnNMR Spectroscopy of PtBr(BrSnMel)( l-Cl&decomposition begins within 15 min to generate the free ligand NMe+C,N)z (2). The complex PtBr(BrSnMel)( l-CloH6CloH7NMe2-8and unidentified Pt-containing products. The PtNMe+C,N)2 (2) can be formed in situ by mixing equimolar (IV) hydride Pt(OOCCF3)(H)( ~ - C I O H ~ N M ~ ~ -(IC) ~ - Ccan , N ) ~ amountsof cis-Pt( l-CloH6NMe2-8-C,N)2andMezSnBrzin CD2be prepared and characterized in situ in an NMR tube reaction C12. It is also present in samples taken at the beginning of reaction of cis-Pt(I - C ~ O H ~ N M ~ ~ - ~with - C an , Nexcess ) ~ of CF3COOH; 2 (MezSnBr2 with cis-€%(1-cloH6NMe2-8-C,N)2). In both see eq 4 in Scheme I. However, attempts to isolatethis chemically cases, the lH and l19Sn NMR spectra also show the resonances unstable product from a large-scale reaction failed. Another of the starting compounds. The presence of a P t S n interaction attempted synthesis of lc from an anion-exchange reaction of l b in 2 is clearly shown by the l19Sn NMR spectrum (see with AgOOCCF3 was similarly unsuccessful. Complexes l a and Experimental Section) in which the resonance at -49.2 ppm has l b have been characterized by IH NMR, IR, and elemental a IJ( 19sPt,119Sn) value of 13 070 Hz, which lies in the large range analysis. These are the first isolable aryl-Pt(1V) hydrides. The of 2-35 kHz known for Pt-Sn coupling constant^.^^ This Pt-Sn complexes are off-white neutral species with reasonable solubility interaction is alsoclear in the IH NMR spectrum, in which several in chloroform and dichloromethane. Me resonances exhibit both Sn and Pt satellites. For Sn-Me 1H NMR and IR Spectroscopy of the Pt(IV) Hydrides 1. The groups, two singlets are found at 0.47 ppm (2J(Sn,1H)= 55 Hz) IH NMR spectra of 1 (see Table I) show all the characteristics and 1.21 ppm (2J(Sn,1H)= 51 Hz; 3J(195Pt,lH)= 6 Hz), and of an asymmetric octahedral structure. For the -NMe groups, for the -NMe groups, there are four singlets at 2.02,2.97,3.68, there are four singlets; two of them are somewhat broadened and and 3.99 ppm. The former two singletsof the-NMe groups have the other two have distinct Pt satellites. One can deduce that the both Pt and Sn satellites (3J(195Pt,1H) = 10 Hz, 4J(Sn,1H)= 17 naphthyl ligands are positioned mutually perpendicular, since in Hz; 3J(195Pt,1H) = 6 Hz, 4J(Sn,1H)= 13 Hz), whereas the other the aromatic region there is an upfield shift for one of the ortho two have only Pt satellites (3J(195Pt,1H) = 6 Hz, 3J(195Pt,1H) = protons; i.e., it is held near the aromatic ring of the second naphthyl 20 Hz). The aromatic region shows a multiplet at ca. 7.4 ppm, ligand. The ortho proton of the latter shows no extreme up- or a triplet at 6.88 ppm (4J(195Pt,lH)= 14 Hz), and a doublet at downfield shifts. Besides these signals for the two C,N bonded 6.07 ppm (3J(19sPt,lH)= 43 Hz), pointing to a perpendicular naphthyl ligands, there is a distinctiveupfield resonance at -20.4 orientationof the naphthyl ligands. For 2, two structural proposals ppm (1H) with a large 1J(195Pt,lH)value of ca. 1550 Hz (1610 (see Figure 1) can be made. Structure a is a Pt(1V) complex in Hz for IC). These data are characteristic for a hydride ligand which the Sn-Br bond is oxidatively added to the Pt center, as that is trans to a nitrogen ligand on a Pt(1V) center.30 This found for PtCl(ClzSnMe)( 1-Cl~I-&NMe2-8-C,N)2?4 and structure trans-N position of the hydride in 1 is to be expected, since the b is a Pt(I1) complex in which the Sn-Br bond is side-on Ndonor ligands have a lower trans influence than C-donor ligands. coordinated to the Pt center and consequently lengthened, as in Literature data for Pt(1V) hydrides, prepared in situ, show that I~(~B~S~B~M~~)(C~H~CH~NM~Z-~-C,N)(COD) (p-Bran = Pt coupling constants are normally in the range 650-1 250 H z , ~ ~2.934 ~ ~(1)~A vs Sn-Br = 2.608 (1) A).17We have been unable but these compounds have halides, phosphines, or cyanides as trans ligands. Separate evidence for complexes 1 being Pt(1V) (31) Monochromatic X-ray photoelectron spectroscopy was used for deterspecies comes from two different sources. First, XPS measuremination of the Pt 4f binding energy of the Pt center in Ib. Apparatus and methods are described in the publication about the XPS measurements show the Pt center to have the oxidation state 4+.31 Second, ments of the F't complexes PtX[CaH3(CH2NMe&-2,6]: Muijsers, J. complex l b can be independently synthesized from the Pt(1V)

Scheme I. Synthetic Routes for RX(H)( I - C I O H ~ N M ~ Z - ~ - C , N ) ~

C.; Niemantsverdriet, J. W.; Wehman-Ooyevaar, I. C. M.; Grove, D. M.; van Koten. G. Inorg. Chem. 1992, 31,2655. ( 3 2 ) Green, M.; Howard, J. A. K.; Proud, J.; Spencer, J. L.; Stone, F. G. A.; (29) A tin-carbene moiety is expected to form a polymeric material, as was Tsipis, C. A. J. Chem. SOC.,Chem. Commun. 1976, 671. proposed for the byproduct of the decomposition reaction of the I r S n complex Ir(p-BrSnBrMe2)(C6H~CH2NMe2-2-C,N)(cycloocta-1,5-di-(33) (a) Holt, M. S.; Wilson, W. L.; Nelson, J. H. Chem. Rev. 1989,89, 11. (b) Ghilardi, C. A,; Midollini, S.; Moneti, S.; Orlandini, A,; Scapacci, em).'' G.; Dakternieks, D. J. Chem. Soc., Chem. Commun. 1989, 1686. (c) (30) (a) Anderson, D. W. W.; Ebsworth, E. A. V.; Rankin, D. W. H.J. Ammann, C.; Pregosin, P. S . ;Riiegger, H.; Grassi, M.; Musco, A. Magn. Chem. Soc., Dalton 1073, 854. (b) Blacklaws, I. M.; Brown, L. C.; Reson. Chem. 1989, 27, 355. Ebsworth, E. A. V.;Reed, F. J. S. J . Chem. Soc., Dalton Trans. 1978, (34) Smeets, W. J. J.; Spek, A. L.; van Beek, J. A. M.; van Koten, G. Acta 877. (c) van der Zeijden, A. A. H.; van Koten, G.; Luijk, R.; Grove, Crystallogr. 1992, C48, 745. D. M. Organometallics 1988, 7 , 1556.

5488 Inorganic Chemistry, Vol. 31, No. 26, 1992 Table I.

Wehman-Ooyevaar et al.

IH NMR Data for the Hydride Complexes P~X(H)(I-CIOH~NM~~-~-C,N)~ (1)'

X C1 ( l a ) Br (lb) OOCCF3 (IC)

aryl H 6.14d ( 5 8 ) , 6.92 t (13), 7.26-7.94 m 6.1 1 d (60), 6.92 t (14.5). 7.1 5-7.92 m 6.01 d (60). 6.87 t (14.5), 7.25-8.0m

NMez 2.18 s (12). 3.31: 3.55 s (23), 3.606 2 . 1 5 ~ ( 1 2 ) , 3 . 4 4 , ~ 3 . 5 7 ~ (3.706 24), 2.19 s ( l l ) , 3.18: 3.43,b 3.50b

Pt-H; IJ('95Pt,'H), HZ -20.39 S; 1569 -20.35 S; 1540 -19.37 S; 1610

Recorded in CDCI3 at room temperature; 8 in ppm relative to external TMS; "J(lg5Pt,lH) in Hz in parentheses. Broad resonance; 3J(195Pt,1H) not observed.

With cis-Pt( ~ - C I O H ~ N M ~ ~ - ~the - Cacidic , N ) ~alcohol , CF3CH2OH gives the same reaction as MeOH; Le., PtBr(l-c~&NMe2-8-C,N)( l-CloH6NHMez-8-C,H) is formed in good yield. When less acidicEtOH is used, this zwitterionic hydrogen complex is formed, but now in a 1:l mixture with the Pt(1V) hydride lb. a (~t'") b (Pt") From t-BuOH, with a low pKa value, the main product is the Pt(1V) hydride l b and only 16% of the zwitterionic hydrogen Figure 1. The Pt(1V)Sn complex (a) versus the Pt(I1)Sn complex (b) species is formed. From these results one can clearly see that as possible structures for 2. product formation is directly related to the alcohol pKa. To Table 11. Products and Yields from the Reactions of determine the hydride source in the t-BuOH reaction, the cis-Pt( 1- C I ~ H ~ N M ~ ~ - ~ -or C ,cis-Pt(CsH,CHzNMe2-2-C,N)2 N)Z with deuterated alcohol t-BuOD was used and this gives a 3: 1 mixture Me2SnBr2 in 6-1O:l Mixtures of C H Z C ~ ~ / R O H ( D ) ~ of lband IbD, withonly tracesof PtBr( l-cloH6NMe2-8-C,f'V)(lcis-Pt( 1Cl&NDMe2-8-C,D); no PtBr( 1-CIOH~NM~Z-~-C,N)( l-CloH6C 1oH6NMezNHMe2-8-C,H) was formed. This result shows that Pt(1V) 8-C") cishydride formation occurs without direct interferenceof the added tot. Pt(C6H4CH2NMe2alcohol, in this case tert-butyl alcohol. yield, 2-cmz When the starting Pt complex is the less rigid complex cisROH(D) pK. lbH+b % ' yield of H+ ' P ~ ( C ~ H ~ C H Z N M ~ ~ - the ~ - Creaction , N ) ~ , with Me2SnBr2 and 1 43' 60' CSH~~*~ t-BuOH affords only the zwitterionichydrogen complex, i.e. PtBr5:l 33f C6D6d.s (C6H4CH2NMe2-2-C,N)(CsH4CH2NHMe2-2-C,H). However, 15.5 1 95 90 MeOH thesameproduct, not theexpected Pt(1V) hydride, isalsoobtained 1h 67 MeOD when the reaction is carried out in dry benzene. This result and 15.9 1:l 88 EtOH 12.4 1 76 CFjCH2OH its consequences for the mechanistic proposals are dealt with in 5 : 1f 41 75' 18 t-BuOH the Discussion. 3:1f.i f-BuOD' C. R e a c t i o ~of cis-Pt( l-Cl&IdWe~-&C,iV)z with HX (X = No P t S n intermediates were observed during the reaction unless Cl, OOCCF3). The product resulting from treatment of a CDC13 stated otherwise. * H+ = PtBr( l-CloHsNMez-8-C,N)( l-CloH6NHMczsolution of cis-Pt( l-Cl&NMe2-8-C,N)2 with an excess of HX 8-C,H). H+ ' = PtBr(C6H,CH2NMc2-2-C~(C6H4CH2NHMe2-2depends strongly on the anion X. When X = C1, the zwitterionic C,H). d Used as solvent. Neither CHzClz nor ROH is present. e After hydrogen complex PtCl( ~ - C I O H ~ N M ~ ~ - ~l-CloH6NHMe2-CJV)( ob60 h of stirring. f P t S n intermediate (PtBr(SnBr(Me)2)(L-C,N)z) 8-C,H) is formed, together with a previously identified product, served during thereaction. 8 After 24 hofstirring. * PtBr( l-CloH6NMe2which results from a subsequent reaction with excess HC1.I In 8-C,N)(l-CloHsNDMe2-8-C,D)(=D+) instead of H+. lb-D instead of H+; traces of D+ present. contrast, the reaction of CSCOOH with cis-Pt( I-CloH6NMe28-C,ZV)2 gives the hydride complex ICas the main product (see eq 4 in Scheme I) and only traces of the zwitterionic hydrogen to isolate 2 in a pure form but believe, on spectroscopic grounds, complex Pt(OOCCS)( 1- C I O H ~ N M ~ Z - ~ - C -CloH6NHMe2,N)(~ that it has structure a. First, J(195Pt,lH)values in the IH NMR 8-C,H). spectrum of 2, especially those in the aromatic region, are D. MOCdculatiom. Using thesystems trans-[PdCl(H)(Me)2indicative for a Pt(1V) rather than a Pt(1I) complex. Second, the (NH3)--NH3] and trans- [PdCl(Me)2(NH+H-NH3] as models Sn chemical shift of -49.2 ppm for 2 points to a tetrahedral for l a and PtCl( 1- C I O H ~ N M ~ ~ - ~ -1C -CloH6NHMez-l-C,ff), ,N)( geometry of the Sn center; cf. 6(Sn) = -50 ppm for the Pt-Sn respectively, SCF and C A S S C F calculations indicate that A, complex [(N(CHzCH2PPh2)3]Pt(SnMe3)][BPh4].33b Last, the the five-coordinate zwitterionic palladium(I1) system, is the lowest NMR data do not compare favorably with those of the iridium point on the energy hypersurface (or close to it), since other complex Ir(p-BrSnBrMe2)(C&CH2NMe2-2-CJV)(COD),which geometrical deformations from A resulted in a net destabilization has trigonal bipyramidal tin geometry (type b); 6(Sn) = -161.6 of the system; see Chart I.36 In particular, the five-coordinate ppm (see Experimental Section) with 2J(Sn,1H)values for the palladium(1V) hydride system F, which does not experience any Sn-Me groups of 60 and 49 Hz.17,35 interaction with NH3, is destabilized by 25.6 kcal/mol. When B. Reactioasof cis-Pt(1-Cl&IdWez-8-C,N)zor cis-Pt(C6H~ NH3 remains in thevicinity of the Pd-H bond, thedestabilization CHZNMQ-~-C,N)~ with Me&nBrz in CHzClzIROH (R = Me, is lower, however (see for instance D).37 Et, CF~CHZ,t-Bu). Without MeOH, the reaction of cis-Pt(1The analysis of the wave function of A reveals the nature of Cl~H6NMe~-8-C,N)2 with Me2SnX2 affords the hydride 1 the Pd-SH-N linkage. The two bonding orbitals c and d are whereas, with MeOH, the same reaction provides the tautomeric shown in Figure 2.38 Orbital c is the bonding combination of the zwitterionic hydrogen complex PtX( ~ - C I O H ~ N M ~ ~ - ~1-- C , N ) ( CloH6NHMe2-8-CJI).1 Toextend our study into the mechanism (36) Computed CASSCF total energies (in au; 1 au = 627.5 kcal/mol): A, of these contrasting reactions, alcohols other than MeOH with -5578.3535; B, -5578.2799; C, -5578.2382; D, -5578.3453; E, -5578.3393; F, -5578.3127. In these calculations, six electrons in six varying steric and electronic properties have been used in the active orbitals were correlated. These active orbitals were chosen 80 as specific reaction of cis-Pt( ~ - C I O H ~ N M ~ Z - ~ and - C , Ncis)~ todescribethePd-HandN-Hbonds,theother4dorbitalofal symmetry P ~ ( C ~ H ~ C H ~ N M ~ Z - with ~ - C MezSnBrz. ,N)Z The results (prod(in the C, symmetry point group), and the 5s orbital of Pd. (37) An optimum distance of 1.32A is found for the approach of NH3 toward ucts and yields) are shown in Table 11. ~

~

~

(35) Jastrzebski,J. T. B.H.; Grove, D. M.;Boersma, J.; Ernsting, J.-M.; van Koten, G. Magn. Reson. Chem. 1991, 29, 25.

the platinum hydride. This geometry is destabilized by 4.8 kcal/mol with respect to A. (38) TheseorbitalsaredoublyoccupiedintheSCF wave functionandstrongly occupied in the CASSCF wave function.

Inorganic Chemistry, Vol. 31, No. 26, 1992 5489

An Organoplatinum-Amine System Energy Levels (Underlined) and Bond Distances (Italic) of the [PdCl(Me)2(NH3)-.H-NH3] Systemu

Chart I.

10.00

+72.4

1

7.50-

5.00C

+46.2

3

2.50-

v

0.00-

+25.6

-2.50-5.00-

F +13.0

-7.50-

- l O . O O ~ ,, , , -1O!OO

1

;, ,

-7150

1

,

-5!00

I

h,0.00 ,

-2150

,

[

I

,

I

I

I

I

2.50

,

I

,

,

,

I

5.00

I

I

1 ,

7.50

I

/

I

1 00

(a.u.)

Figure 3. Molecular electrostatic potential map of the deprotonated

-

[PdCI(Me)2(NH+NH$ system. The most negative contour line (around the minimum) is at -0.290 au, and the contour values increase from this value to 0.090 au (the value of the most internal dotted line) by steps of 0.020 au. For the sake of clarity, the two methyl ligands pointing out of the plane of the map have been omitted.

4.1

A

Relative energies in kcal/mol; bond distances in

Pd

H

N

Pd

C

A.

H

N

d

Figure 2. Thc two bonding orbitals c and d.

4d,2 with the U*N-H orbital and is almost entirely localized on the

palladium atom. A Mulliken population analysis indicates that it has 88% of the electronic density on Pd, 3% on H, and 6% on N. Moreover there is no hybridization of 4dz with 5s and 5p,: the contributions of 5s and Sp, to c are only 1% and 0.7%, respectively. Orbital d, bonding UN-H, remains largely localized on N-H (95%). The interaction between the Pd orbitals and the NH3 orbitals is therefore quite minimal and probably best described as a 4e-3c interaction due to the absence of the empty 5s and 5p, orbitals in the bonding scheme. Conversely the electrostatic (or ionic) type interaction in the zwitterion is maximized. A clear-cut indication of this feature is given by an electrostatic potential map computed for the deprotonated [PdCl(Me)2(NH+NH3]-system (with the previously optimized Pd-N distance of 3.03 A) (see Figure 3); a negative area is found between the Pd and the N atoms. Moreover, its minimum corresponds precisely to the position of the proton in A. When NH3 is displaced toward the C1 atom, this minimum is also displaced but stays on the Pd-N axis (in this case the energy of the corresponding protonated system is slightly lowered, by 6.8 kcal/mol for a 30" bending). A similar map has been determined for the cis-[PdCl(Me)2(NH3)--NH3]-isomer and does not reveal any significant difference with the map obtained for the trans isomer. In contrast, the Pd( IV) hydride system has a Pd-H bond which is, as expected, quite covalent in character. This is best seen from the two orbitals which describe this bond in the CASSCF wave function. The 4d,2 + SH bonding combination which is strongly occupied (occupation number of 1.88 e) has 60% of the electronic density on Pd and 38% on H. The correlating weakly 4 d Z 2 - s ~ antibonding combination (with an occupation number of 0.12 e) has 40% of the electronic density on Pd and 52% on H.

All these features are therefore consistent with the fact that, in the Pd(II)-H-NH3 system, the electrostatic (or ionic) component is the main contributor to the M-OH-N interaction energy, at least in the palladium systems. Calculations for the Pt analogs show that the orbital interactions play a somewhat greater role in the stabilization: now, in c, 76% of the electronic density is localized on Pt, 3% on H, and 8% on N. In d, 89% of the electronic density is localized on N-H. The corresponding Pt-H overlap population, which can be taken as a measure of the orbital interactions, has increased to 0.34 e from 0.15 e in the Pd system. In the Pt case, one also observes a greater participation of the s and p, empty orbitals in the bonding. More specifically, in c the d s orbital is hybridized with the empty s orbital, the respective participations being 62% for dz and 12%for s. In this sense, the Pte-H-N linkage has more bonding character than the Pd-OH-N interaction. All these features are reflected in the energeticsof the interaction: in the platinum case,the stabilization gained on going from a metal-hydrogen distance of 10 A to a metal-hydrogen distance of 2.01 A is greater; it amounts to 88.5 kcal/mol at the RECP-SCF level of theory, whereas the value for the Pd system at the same level of theory is 65.5 kcal/mol. E. Reactions of the Hydride Complexes 1 and PtX( l-Cl&NMe+CJV)( l-C~~HdrJHMe&C' with Alkynes. The hydridecomplexes 1and the zwitterionichydrogen complexesPtX( 1C I o H ~Me2-8-C,N) N ( 1-C loHsNHMe2)-8-C,H) have been investigated as potential starting compounds for the synthesis of alkyl or alkenyl complexes. To this end, reactions of these complexes were carried out using a variety of alkenesor acetylenes, with differing electronicand steric properties, Le. ethene, styrene, neohexene, methyl methacrylate,vinyl acetate, dimethyl maleate, phenylacetylene, diphenylacetylene, and dimethyl acetylenedicarboxylate. Of these, only the last showed any reactivity and then only with the CF3COO-complexes IC and Pt(OOCCFj)( 1C I ~ H ~ N M ~ ~ - ~ -1-CloHaNH C J V ) ( Mez-8-C,H). Both reactions afford the same Pt(IV) alkenyl product, i.e. Pt(OOCCF&IC(COOMe)=CH(COOMe))(I - C I O H ~ N M ~ ~ - ~ - C , I Vsee )~ (3); Scheme 11. The IH NMR spectrum (see Experimental Section) of this product shows that the 2 isomer is stereoselectively formed; the

5490 Inorganic Chemistry, Vol. 31, No.26, 1992

Wehman-Ooyevaar et al.

l-CloH6NHMez-8-C,H) with Dimethyl Scheme 11. Mechanism of the Reactions of 1 and Pt(OOCCFs)( l-C1~H6NMe~-8-C,N)( Acetylenedicarboxylate"

"

\ \ 3 or its enantiomer

1c 0

i = +MeOOCC=CCOOMe.

chemical shift valueof the olefinicproton is 6.5 Although the 3J(195Pt,1H)value of 77 Hz for the alkenyl proton seems to be relatively small for the Z geometry, this is not a Pt(I1) species and the value is consistent with a Pt(1V) complex. Furthermore, the IH NMR spectrum shows four singlets with Pt satellites for the -NMe groups, two singlets for the -OMe groups, and an aromatic pattern similar to that of 1. On the basis of this evidence, 3 is proposed to have the structure shown in Scheme I1 with a general Pt geometry related to that of 1.

I b (XI Er)

cTN .

&"

V

Y-R,X

Discussion Formation of the Hydride Complexes l a and lb. Mechanism of the M Q S ~ XReaction. ~ The complexes 1 are the first isolable aryl-Pt(1V) hydride species to be characterized. In the literature Pt(1V) hydrides have often been proposed as intermediates in catalytic cycles and they have sometimes been detected in solution by spectroscopic measurement~.30a-~@ The formation of hydrides 1 in reaction 2 (cis-Pt(l-C&NMe2-8-C,N)2 with Me2SnXz) was unexpected. Usually, reactions of square planar ds organometalliccomplexes with Sn(1V) reagents lead to oxidative addition products or to side-on coordination of the Sn-Y (Y = halide, alkyl, aryl, or hydride) bond to theds metalcenter.17v33a+41 In the first stageofthereaction affording 1, we have good spectroscopic evidence for a complex containing a P t S n moiety and we believe the first step toward 1 is indeed an oxidative addition of MezSnXz to the Pt center to form 2 see eq 5 . As to be expected for MezSnXz, an electronpoor Sn(1V) reagent, thestereochemistryof this oxidativeaddition reaction results in a cis geometry. Literature examples show that oxidative addition of a Sn-X bond can result in either trans or cis geometries, depending on the electron density on the Sn atom. For example, the reaction of SnBr4 with cis-Pt(l-cl0H6NMe2-8-C,N)2 results in a trans oxidative addition whereas reaction with the less strong Lewis acid MeSnC13 results in a cis ~~~~

(39) (a) Clark, H. C.; Ferguson,G.; Goel, A. B.; Janzen, E. G. Rlegger, H.; Sew,€'. Y.; Wong, C. S. J. Am. Chem.Soc. 1986,108,6961. (b) Reger, D. L.; Baxter, J. C.; Garza, D. G. Organometallics 1990, 9, 16. (40) (a) Ebsworth, E. A. V.; Henderson, S. G. D.; Rankin, D. W. H. Inorg. Chim. Acta 1981, 48, 159. (b) Jones, R. F.; Cole-Hamilton, D. J. J . Chem. Soc., Chem. Commun. 1981, 1245. (41) (a) Kuiper, J. Inorg. Chem. 1977, 16, 2171; 1978, 17, 77. (b) Butler, G.; Eaborn, C.; Pidwck, A. J . Organomet. Chem. 1979, 181, 47. (c) Packett, D. L.; Syed, A.; Trogler, W. C. Organometallics 1988, 7. 159. (d) Schubert, U.; Kunz, E.; Harkers, B.; Willnecker, J.; Meyer, J . J . Am. Chem. SOC.1989, I l l , 2572.

oxidative a d d i t i ~ n . Complexes ~ ~ , ~ ~ ~ like 2 with a M a n bond are often labile and, for example, the complex [ { N ( C H Z C H ~ P P ~ ~ ) ~ J Pt(SnMe,)][BPh4] in solution is only stable for a few hours.33b Complex 2 in solution reacts further to form the Pt(1V) hydride 1with elimination of a tin-containing byproduct. In the literature there are precedents for such reactions involving both a-elimination (for example, PtBr(SnBr3)( 1-C,oH6NMe2-8-C,N)2forms the complex truns,cis-PtBrz( l-CloH6NMe~-8-C,N)2 by eliminating and (for example, I+B~S~B~M~~)(C~H~CHZNM~Z-~-C,N)(COD) forms CaHsCHzNMez and [I~CI(COD)]Z via an Ir(II1) hydride intermediate)." Since the product of the decomposition of 2 is a hydride, we believe the &elimination route, in which the hydride atom is derived from an Sn-Me group, is operative. Experimentsin C6D6 confirmed that the solvent was not the hydride source. In this @-eliminationfrom one of the PtSn-CHs units of 2 (see q 5 ) , a carbene complex [BrSn(CHz)Me] should be formed.29 In our study, the tin-containing complex was found (by lI9Sn NMR spectroscopy) to also contain platinum, and this helps explain the low yield of the hydride obtained by method a. Further evidence that the Pt(1V) hydrides result from a &elimination reaction is given by the reaction of cis-Pt(1-Cl0H6NMez-8-C,N)z with Ph2SnC12, which stops at the stage of a P t S n complex like 2: a &elimination, in this case from a phenyl group which would give a benzyne, is not likely. The bromo hydride complex l b could also be synthesized via another route, Le. from the reduction of cis,cis-PtBrz( 1-c10H6(42) (a) van Beek, J. A. M.; Grove, D. M.; Smeets, W. J. J.; Spek, A. L.; van Koten, G. To be published. (b) This process in the proposcd route (eq 5) involves B free coordination site created by either Pt-X or Pt-N dissociation. This detail of the 0-elimination process is being studied further.

An Organoplatinum-Amine System

Inorganic Chemistry, Vol. 31, No. 26, 1992 5491

place to form the corresponding Pt(1V) What we NMe&C,N)z by n-Bu3SnH in the presence of azobis(isobupropose (see eq 6) is that this hydride PtBr(H)(CsH&HzNMeztyronitrile) (abbreviated as AIBN) (eq 3). This organometallic 2-C,N)2 is an intermediate which can now isomerize, because of reaction resembles the well-documented reductions of organic the presenceof the flexible-CHzNMezmoiety, to the morestable halides by organotin hydrides that are very useful in organic tautomer P~B~(C~H~CHZNM~Z-~-C,N)(C~H~CHZNH synthesis.43 The use of AIBN is simply to accelerate the reduction C,H). With the [C6H4CHzNMez-2]-ligand, the N-donor atom that (in organic systems) is known to usually involve freeradical intermediates. A further analogy of cis&-PtBrz( 1- C I ~ H ~ N M ~ Z -can move away from the platinum center and rotation of 180° around the Cipo-Cparaaxis can take place. This is not possible 8-C,N)zto organic halides is that only monoreduction takes place in 1, where the rigid naphthyl skeleton always keeps the nitrogen with this reagent; cf. reduction of cc14 to CHCl3 and not CHzatoms within the Pt coordination sphere; isomerization of 1to the ci2.44 zwitterionic hydrogen complex PtX( ~ - C I O H ~ N M ~ Z - ~1-C,N)( Formation of the Hydride Complexes 1versus the Zwitterionic CloH6NHMez-l-C,H) has never been observed or induced. HydroSeo Cm@xm ~ ( 1 - C i o b ” M d - C ( W o & ” H M ~ Interestingly, the C A S S C F energy difference between F and 8-Ca. For selective formation of the zwitterionic hydrogen the Pd(1V) hydride system [Pdcl(H)(Me)z(NH3)~]~~ (in which complexes, a proton source is necessary, and we have shown that the remote NH3 of F now occupies the sixth coordination site the reaction of RzSnXz with ROH, assisted by the presence of trans to the hydride) is computed to be 12.6 kcal/mol, (see Chart Pt(I1) aminespecies, generates HX.I For the formation of Pt(1V) I), thus indicatingthat (as expected from the strong trans influence hydrides the first step in the reaction of RzSnXz with the Pt(I1) of the hydride) the dissociation of an axial amine type ligand is species is formation of a P t S n complex (2). In all reactions relatively easy, at least in the Pd(1V) model complexes. where ROH is present, there are thus two competitive reactions with markedly different reaction rates and the dominant path is The Nature of the M-H-NHJ Linkage and the Relative Stability seen to be dependent on the pKa value of ROH (see Table 11). of the Zwitterionic Hydrogen System and Its Hydride Tautomer. More acidic alcohols (CF~CHZOH, MeOH) promote formation How do the present theoretical results for the M-nH-NHs (M of the zwitterionic hydrogen species whereas a weaker one (t= Pd, Pt) system compare with the experimental results and BuOH, EtOH) also allows Pt(1V) hydride formation and gives other theoretical studies? In their review article, Green and rise to a product mixture. The fact that CF3CHzOH and EtOH Brookhardt characterize the agostic interaction as a two-electron give such different results also shows that steric factors are not donation of the u C-H bond to an empty metal orbital.6b This playing an important role. In the mechanism to form the hydrides, results in a bent M-H-C geometry. In the zwitterionic species the second step, &elimination, does not seem to be adversely we have studied, i.e. P ~ B ~ ( ~ - C I O H ~ N M ~ Z - ~ - C , N ) ( ~ affected by the presence of a protic solvent and complex 2, for NHMe+C,H), the Pt-SH-N linkage is almost linear, as it is example, was identified spectroscopically in the presence of in the [(PtC14)-ci~-PtClz(NH~Me)#-dianion, where Orpen et t-BuOH. The experiments with t-BuOD give further insight into al. also favor a 3c-4e description (with an electrostatic compothe role of protic solvents. The formation of small amounts of nent).8 Note that, in our complexes and that of Orpen et al., an the deuterated zwitterioniccomplex is consistent with the t-BuOH anionic entity is involved. Another characteristic of agostic bonds reaction and the formation of a small amount of acid. However, is that they are easily displaced by a nucleophile.6b However, although the presence of significant amounts of the Pt(1V) there is no indicationof such behavior in our zwitterionichydrogen deuteride alongside the Pt(1V) hydride seems to suggest that the complexes. Finally, there is an important gain in stabilization solvent is also playing a role in the step from the P t S n complex energy on going from C to A of 72.4 kcal/mol (the stabilization 2 to the final product; this is not the case. The deuteride results is even greater for the platinum system; see above), i.e. much from proton/deuterium exchange of the originally formed Pthigher than the 5-1 5 kcal/mol usually expected (experimentallf’ (IV) hydride with t-BuOD; such exchange reactions are welland theoreti~ally~~) for an agostic type of interaction. known for terminal metal hydrides in the presence of protic One can now consider the role of an extra two-electron-donor solvents.45 ligand on the energy difference between the Pt(1V) hydride system The results of the reactions of C~~-P~(C~H~CHZNM~Z-~-C,N)Z and the zwitterionic hydrogen Pt(I1) complex. To this end with MezSnBrz (see Table 11) contrast markedly with those of calculations were performed on the model system with an extra cis-Pt( 1- C ~ O H ~ N M ~ ~ - ~the - Czwitterionic ,N)~; hydrogen complex NH3 group; the results are shown in Chart I1 (for the sake of P~B~(C~H~CHZNM~Z-~-C,N)(C~H~CHZNHM~Z-~-C,H) is alcomparison, the systems of this chart and those of Chart I are ways formed, never the corresponding tautomeric Pt( IV) hydride. positioned in a similar way).49 One sees that the addition of an The mechanism to explain this begins, as for CiS-Pt(l-C&,extra ligand brings extra destabilization, except for the sixNMe+C,N)z, with the formation of a P t S n complex (see eq coordinate Pd(1V) hydride system. This is now comparatively 6), which is indeed observed by IH NMR spectroscopy during less destabilized than the five-coordinate Pd(1V) hydride with respect to the zwitterionic hydrogen Pd(I1) isomer (compare for Me2f3rSn H instance the destabilizationof F with respect to A, which amounts to 25.6 kcal/mol, and the destabilization of E’with respect to A’, which amounts to 12.8 kcal/mol). This 12.8 kcal/mol energy difference between the six-coordinate Pd(1V) hydride complex and the five-coordinate zwitterionic hydrogen Pd(I1) complex makes formation of the former via the use of an electron-donating group most unlikely, unless differential solvation effects-not

the reactions. Then, in the next step the @-eliminationtakes (43) For example: (a) Menapace, L. W.; Kuivila, H. G. J. Am. Chem. SOC. 1964,86, 3047. (b) Grady, G. L.; Kuivila, H. G. J . Org. Chem. 1969, 34, 2014. (44) Wilkinson, G.; Stone, F. G. A.; Abel, E. W. Comprehensive Organometallic Chemistry; Pergamon Press: New York, 1982; Vol. 2. (45) (a) Baker, M. V.;Field, L.D. Organometallics 1986,5,821. (b) Park, S.;Johnson, M. P.; Roundhill, D. M. Organometallics 1989, 8, 1700.

(46) The C A S S C F energy of [PdCI(H)(Me)2(NH1)2] is -5578.3328 au. (47) (a) Lichtenberger, D. L.; Kellog, G. L. J . Am. Chem. Soc. 1986,108, 2560. (b) Gonzalez, A. A.; Zhang, K.; Mukerjjee, S.L.; Hoff, C. D.; Khalsa, G. R. K.; Kubas, G. J. ACS Symp. Ser. 1990, 428, 133. (48) (a) Koga, N.; Obara, S.;Kitaura, K.; Morokuma, K. J . Am. Chem. Soc. 1985,107,7109. (b) Koga, N.; Morokuma, K. J . Am. Chem.Soc. 1988, 110, 108. (49) C A S S C F energies (in au): A’, -5634.4909; B’, -5634.4506; C’, -5634.3 160;IY,-5634.4657; E’,-5634.4705. In thesecalculations eight

electrons in eight active orbitals were correlated. This active space was obtained by adding to the active space described in ref 36 the lone pair of the second NH3 ligand and its antibonding combination with 4 d ~ .

Wehman-Ooyevaar et al.

5492 Inorganic Chemistry, Vol. 31, No. 26,1992

Chart 11. Energy Levels (Underlined) and Bond Distances System" (Italic) of the [PdCl(H)(Me)2(NH3)2.-NH3] + Z 8

I pd I

NH,(

??:':

.........H-NH, 'O'O

C'

+46.2

8'

H

-

E'

8-C'.

0.0

A' a

Relative energies in kcal/mol; bond distances in

Scheme 111. Mechanism of the Reaction of cis-€%( l-CloH6NMez-8-C,N)2with HX

I

n

7.02

of the Pt center on the H+ cation to form the five-coordinate square pyramidal Pt(IV) complex [PtH( 1-CIOH~NM~Z-8C,N)z]+. The other involves a nucleophilic attack of the anion on an empty Pt orbital, and this is attended by nitrogen ligand dissociation and protonation. The second pathway (see eq 7a in Scheme 111) was proposed as the operating mechanism for the formation of the zwitterionic complex R X ( 1-Cl&NMe2-8C f l ( l-CloH6NHMe2-8-C,H).' Formation of the hydride complex IC,containing a Pt(1V) center, is more in linewith an oxidative addition reaction. However, in this case also, we propose nucleophilic attack of CF3COOH on the metal complex attended by nitrogen dissociation. The fact that N protonation does not take place can be probably explained by the bridging character of the acetate group that ''protects" the hydride during its formation; see the proposed intermediate in eq 7b in Scheme 111. A precedent for such an intermediate comes from the reaction of c ~ s - P ~ ( C ~ H ~ C H Z N M ~ Z -with ~ - C Hg(00CMe)2;s0 ,N)~ an X-ray structure shows that the product, i.e. Pt(pMeC02)(HgOzC M ~ ) ( C ~ H ~ C H ~ N M ~ ~ - ~possesses - C . N ) Zan , acetate group bridging over and stabilizing the Pt-Hg interaction. Reactivity of the Hydride Complexes 1 rad the Zwitterionic

A.

YComplews ~ ~(~-CIOHSNM~-~CZN)(~-G~%NJM In the reactionsof 1andPtX(l-CloHsNMe2-8-C,N)(1-

CloHaNHMe2-8-C,H) with unsaturated reagents, the only reaction observed takes place when the poorly coordinating anion CF3C00-i~present, i.e. when a free coordination site is available. The fact that IC and Pt(OOCCFs)( I-CloH6NMe2-8-Cfl(lCl&NHMe2-8-C,H) only reacted with dimethyl acetylenedicarboxylate shows that a highly activated unsaturated reagent with electron-withdrawingsubstituents is needed, to compte with thecoordinatingabilityoftheanion. Although wehavenotcamed out mechanistic studieson this reaction, the trans stereochemistry of the final product 3 rules out the involvement of a four-center cyclic transition state (see Scheme 11), which could be formed in a concerted addition of the alkyne to IC. This stereochemistry of 3 can be explained by an electron-transfer pracess as proposed earlier for insertion of acetylenes into R-H bonds,39aFirst, after dissociation of the CF3COO- anion and the coordination of the alkyne, electron transfer from the Pt center takes place. This is then followed by transfer of H+ and of the Pt-containing moiety to the acetylene functionality, resulting in formation of 3. This proposal gains support from the fact that the same product (3) is also obtained from the reaction of this alkyne with the zwitterionic hydrogen complex Pt(OOCCFp)( 1-CloH6NMe2-8C,N)(l-CloH6NHMez-8-C,H), which has a bridging hydrogen with a protonic character. However, the Pt(1V) hydride reaction does not go through the zwitterionictransition state (as indicated in Scheme 11); if this were so, rotation of the naphthyl ligand would have to take place, and this is not to be expected (vide supra). Therefore, in view of the fact that 3 is chiral, we think that the product of the zwitterionic reaction is the enantiomeric form of that of the hydride reaction. This is consistent with the fact that both products give the same IH NMR resonance pattern.

taken into account here-turn out to be important. Finally, in the context of the interconversion process, it can be seen that the amine ligand, which is protonated in the zwitterionic system, does not need to depart too much from the coordination sphere to obtain an isomer with a typical palladium-hydride bond length: note, for instance, the relatively low destabilization of D and E with respect to A in Scheme I. R ~ C ~ ~ with O DHX. S Reactions of HX with d8organometallic complexes have been widely reported, and a variety of mechanisms are known."-I3 The reaction of cis-€%(1-C10H6NMe2-8-C,N)2 with an excess of HCl leads to protonation of the ligand and Conclusions formation of the zwitterionic hydrogen complex PtCI( 1-C1&NMe+C,N)( l-CloH6NHMe2-8-C,H),' whereas with CF3From the Pt(I1) speciescis-Pt( l-cloH6NMe2-8-C,N)2and tinCOOH the hydride complex IC is obtained in an oxidative addition (IV) complexes someremarkablystablePt(1V) hydridecomplexes reaction. The Lewis basicity of the anion might be determining containinga rigid C,N-chelating naphthylamineligand have been the reactivity pattern, but it is certainly not the factor that synthesized and isolated. These Pt(1V) hydrides result from a determines the possible type (zwitterionic versus hydridic) of the 8-H elimination from a Pt(I1) intermediate containing a sideresulting complex. This is shown by the fact that the zwitterionic on-bonded Sn-X bond. An oxidative addition approach to such hydrogen complex Pt(OOCCF3)( 1- C I ~ H ~ N M ~ Z - ~(1 -C 'ClOH6,N) hydrides using HX is only successfulwhen X = CFjCOO, because NHMe2-8-C,H) (formed in the reaction of PtBr( l-CioH6NMe2this group can provide anchimeric assistance; with HCl, a 8-C,N)(I - C ~ O H ~ N H M ~ ~ - ~ with - C , WAgOOCCF3) ) does not tautomeric zwitterionic hydrogen-bridged Pt(I1) species results. isomerize to the trifluoroacetate Pt(IV) hydride complex IC. Theoretical calculations show that a Pt( IV) hydride complex is For these reactions of HX with c~s-P~(~-CIOH~NM~Z-~-C,N)Z not as stable as its correspondingPt(II)-H-N tautomer. Despite to form either a zwitterionic or hydridic product, we might propose twocommon mechanistic pathways. One is theoxidative addition (50) van der Ploeg, A. F. M. J.; van Koten, G.; Vrieze, K.; Spek, A. L.Inorg. Chem. 1982, 21, 2014. reaction that begins with nucleophilicattackof the filled d,Zorbital ~

An Organoplatinum-Amine System this stability difference, isomerization from the Pt(1V) hydride to the more stable tautomeric form has not been observed for the naphthylamine ligand system. However, a more flexible benzylamine ligand system allows such an isomerization and only the zwitterionic hydrogen Pt(I1) tautomer has been found from the reaction of C ~ S - P ~ ( C ~ H ~ C H ~ N Mwith ~ ~ - MezSnBr2 ~-C,N)~ in benzene or a mixture of t-BuOH and CH2C12. Although both theoretical and experimental results show no direct relationship between the hydride and zwitterionic tautomers, the fact that both complexesgave the same (enantiomeric) product in a reaction

Inorganic Chemistry, Vol. 31, NO.26, 1992 5493

with dimethyl acetylenedicarboxylate is good evidence that they are chemically related.

Acknowledgment. We are very grateful to Shell Research BV (1.C.M.W.-0.) for financial support. The stay of P.d.V. at the Laboratoire de Chimie Quantique was made possible through a grant from the European Community (Scheme Contract No. SC1-03 19-C (GDF)).The theoretical calculations were camed out at the IBM 3090 of the Centre de Calcul de Strasbourg Cronenbourg.